In Anglo-American nomenclature, a device utilizing breath analysis to detect alcohol and acting on the results are normally referred to as an alcohol interlock, or by the shorter term “alcolock.” The preventive effect of these devices have been demonstrated, along with several positive side effects, especially for the rehabilitation of drivers already convicted for drunk driving, and as a tool for quality assurance of transportation services.
The typical purpose of an alcohol interlock is to prevent drunk driving. Technically, this is implemented by disabling the start of the engine, unless a breath sample with little or no alcohol concentration has been provided. A drunken person with affected driving capability and judgement is thus physically prevented from driving, thereby eliminating possible damage to life and property caused by driving influenced by alcohol. The concentration limit used to determine whether the alcohol interlock enables or disables the vehicle, also called “blocking” or “unblocking”, normally coincides with the legal limit of alcohol consumption allowed for driving.
Regardless of their obvious merits, the idea of alcohol interlocks is somewhat controversial from the point of view of personal integrity and responsibility. A vehicle owner may perceive the alcohol interlock as restricting access to private property, and hence an infringement on personal integrity. In addition, a person accused of drunk driving may claim at least partial irresponsibility, if his or her vehicle was equipped with an alcohol interlock and was still drivable. Both issues of integrity and responsibility touch upon the possibility of false blockings and unblockings.
Suppliers of alcohol interlocks are vague about the influence of inevitable measurement errors, which cause false outputs at a rate depending on the error magnitude. A highly precise instrument will give rise to few false outputs. If many drivers make use of this precision to drive slightly below the limit rather than refraining from driving, the number of intoxicated drivers may increase rather than decrease, thus partly undermining the purpose of alcohol interlocks. On the other hand, a device with a large error will frequently block falsely. If routes to circumvention are introduced to alleviate this problem, the main purpose will again be undermined.
Cost, inconvenience and time consumption are common additional arguments against alcohol interlocks, especially from drivers who are moderate consumers of alcohol. The possibility of circumvention or manipulation, for example, by asking someone else to provide the breath sample or bypassing the interlock, is another problem.